He has to be left in the Repair Section when you dock at base. Do all your handing out of medals, qualifcations and such, then start a new patrol. 90% of the time he'll disappear never to return. (Tho some say they haven't had it happen for theirs) That's how it's always happened for me 100% of the time when he been left in Repair. I've run 4 previous patrols and had the same happen each time. Sadly I was over zealous to install mods while on patrol and lost all 4 careers. The crewmen always show up in thier bunks on the start of a new patrol. If you can find out why and how they do that, that might be the fix for him.
For his replacement I always make sure he's in da bunk or Engine Room. He's never wandered off so far.
